Entelegyne Spiders Research Articles

A spider mating plug functions to protect sperm.

Mating plugs in animals are ubiquitous and are commonly interpreted to be products of mating strategies. In spiders, however, mating plugs may also take on functions beyond female remating prevention. Due to the vagaries of female genital (spermathecal) anatomy, most spiders face the problem of having to secure additional, non-anatomical, protection for transferred sperm. Here, we test the hypothesis that mating plugs, rather than (or in addition to) being adaptations for mating strategies, may serve as sperm protection mechanism. Based on a comparative study on 411 epigyna sampled from 36 families, 187 genera, 330 species of entelegyne spiders, our results confirm the necessity of a sperm protection mechanism. We divided the entelegyne spermathecae into four types: SEG, SED, SCG and SCD. We also studied detailed morphology of epigynal tracts in the spider Diphya wulingensis having the SEG type spermathecae, using 3D-reconstruction based on semi thin histological series section. In this species, we hypothesize that two distinct types of mating plug, the sperm plug and the secretion plug, serve different functions. Morphological details support this: sperm plugs are formed on a modified spermathecal wall by the spilled sperm, and function as a temporary protection mechanism to prevent sperm from leaking and desiccating, while secretion plugs function in postcopulation both as a permanent protection mechanism, and to prevent additional mating. Furthermore, with the modified spermathecal wall of S2 stalk, the problem of shunt of sperm input and output, and the possibility of female multiple mating have been resolved. Variation in spermathecal morphology also suggests that the problem of sperm protection might be resolved in different ways in spiders. Considering mating plugs of varying shapes and origins in the vast morphospace of spiders, we conclude that mating plugs might serve different purposes that relate both to mating strategies, as well as to sperm protection.

Copulatory mechanics of ghost spiders reveals a new self-bracing mechanism in entelegyne spiders.

Spiders evolved a distinctive sperm transfer system, with the male copulatory organs located on the tarsus of the pedipalps. In entelegyne spiders, these organs are usually very complex and consist of various sclerites that not only allow the transfer of the sperm themselves but also provide a mechanical interlock between the male and female genitalia. This interlocking can also involve elements that are not part of the copulatory organ such as the retrolateral tibial apophysis (RTA)-a characteristic of the most diverse group of spiders (RTA clade). The RTA is frequently used for primary locking i.e., the first mechanical engagement between male and female genitalia. Despite its functional importance, some diverse spider lineages have lost the RTA, but evolved an apophysis on the femur instead. It can be hypothesized that this femoral apophysis is a functional surrogate of the RTA during primary locking or possibly serves another function, such as self-bracing, which involves mechanical interaction between male genital structures themselves to stabilize the inserted pedipalp. We tested these hypotheses using ghost spiders of the genus Josa (Anyphaenidae). Our micro-computed tomography data of cryofixed mating pairs show that the primary locking occurs through elements of the copulatory organ itself and that the femoral apophysis does not contact the female genitalia, but hooks to a projection of the copulatory bulb, representing a newly documented self-bracing mechanism for entelegyne spiders. Additionally, we show that the femoral self-bracing apophysis is rather uniform within the genus Josa. This is in contrast to the male genital structures that interact with the female, indicating that the male genital structures of Josa are subject to different selective regimes.

Chromosomal Study on Selected Small Araneomorph Spiders from Brazil, Including the First Records in Palpimanidae and Theridiosomatidae (Araneae, Araneomorphae).

Among the 50,474 spider species, only 849 have chromosomal data available in the literature. Fifty spider families remain unknown from a cytogenetic perspective. The aim of this study was to analyze chromosomally selected araneomorph spiders from Brazil, to contribute to the cytotaxonomy and chromosome evolution of this group. The karyotypes of 12 species belonging to families Corinnidae, Linyphiidae, Oonopidae, Palpimanidae, Theridiidae, Theridiosomatidae, Trachelidae, and Zodariidae were analyzed, including the first chromosomal record for the first two families. Specimens (with the abdomen content partially exposed by perforation) were subjected to colchicine, hypotonization, and fixation. In most cases, the total content of the abdomen was used to prepare slides by spreading of cell suspension and subsequent Giemsa staining. The results were as follows: Cinetomorpha simplex Simon, 1892 (Oonopidae) 2n♂ = 9, X0; Neotrops sp. and Neoxyphinus termitophilus (Oonopidae), 2n♂ = 7, X0; Otiothops birabeni (Palpimanidae); Agyneta sp. (Linyphiidae), 2n♂ = 24, X1X20; Coleosoma floridanum, Thymoites sp.1 and Thymoites sp.2 (Theridiidae), 2n♂ = 22, X1X20; Naatlo sp. (Theridiosomatidae), 2n♂ = 30, X1X20; Orthobula sp. (Trachelidae) 2n♂ = 21, X0; Falconina sp. (Corinnidae), 2n♂ = 28, X1X20; Epicratinus sp. (Zodariidae) 2n♂ = 42, X1X20. The chromosomal morphology was determined for all the samples except for Oonopidae. Most species exhibited telocentric chromosomes, with the exception of Palpimanidae and Theridiosomatidae. The main findings: 1) support an hypothesis on ancestral karyotype of Zodariidae and Oonopidae; 2) reveal a relatively high chromosome number in Palpimanidae that supports an idea on relatively high ancestral chromosome number (2n♂ = 42) of entelegyne spiders (Palpimanoidea is sister group of entelegyne spiders); 3) show that the karyotype found in Theridiosomatidae is exceptional within the Araneoidea.

Embryonic expression patterns of Wnt genes in the RTA-clade spider Cupiennius salei

Spiders represent widely used model organisms for chelicerate and even arthropod development and evolution. Wnt genes are important and evolutionary conserved factors that control and regulate numerous developmental processes. Recent studies comprehensively investigated the complement and expression of spider Wnt genes revealing conserved as well as diverged aspects of their expression and thus (likely) function among different groups of spiders representing Mygalomorphae (tarantulas), and both main groups of Araneae (true spiders) (Haplogynae/Synspermiata and Entelegynae). The allegedly most modern/derived group of entelegyne spiders is represented by the RTA-clade of which no comprehensive data on Wnt expression were available prior to this study. Here, we investigated the embryonic expression of all Wnt genes of the RTA-clade spider Cupiennius salei. We found that most of the Wnt expression patterns are conserved between Cupiennius and other spiders, especially more basally branching species. Surprisingly, most differences in Wnt gene expression are seen in the common model spider Parasteatoda tepidariorum (a non-RTA clade entelegyne species). These results show that data and conclusions drawn from research on one member of a group of animals (or any other organism) cannot necessarily be extrapolated to the group as a whole, and instead highlight the need for comprehensive taxon sampling.

Temperature fluctuations during embryonic development implicated in a naturally occurring instance of abnormal spinnerets in the spider Australomimetus maculosus (Araneae, Mimetidae)

We record developmental abnormalities of the spinnerets in a field-collected adult male specimen of Australomimetus maculosus. These include (1) a supernumerary right posterior lateral spinneret (PLS), (2) ectopic piriform silk gland spigots and tartipores on the left PLS that are normally restricted to anterior lateral spinnerets (ALSs), and (3) what appear to be ectopic ALS sensilla on the left posterior median spinneret (PMS). Published results of teratological experiments and climate data for the collection site indicate that fluctuating sub- and supra-optimal temperatures during embryogenesis may have been responsible for these anomalies. This specimen thus supports the view that spinneret abnormalities, among other aberrations, may be induced when embryos of entelegyne spiders are exposed to fluctuations between high and low temperatures, whether in the laboratory or, as here, in nature. To our knowledge, the ectopic structures seen on the left PLS and left PMS have not been observed previously. Their locations are consistent with a hypothesis by which only the lateral portion of the araneomorph ALS is serially homologous to the PLS, while the remainder of the ALS, along with the colulus/cribellum, is homologous to the PMS.

Hers and his: Silk glands used in egg sac construction by female spiders potentially repurposed by a \u2018modern\u2019 male spider

Cylindrical silk gland (CY) spigots distinguish a large clade of modern spiders, the CY spigot clade, which includes all entelegyne spiders and their closest relatives. Following a widespread paradigm, CYs and their spigots are only known to occur in female spiders and they produce silk used in the construction of egg sacs. Here we report the occurrence of a CY spigot or CY nubbin on each posterior median spinneret (PMS) in males (5th stadium and later) of the spider Australomimetus maculosus. Late juvenile males had a CY spigot on each PMS, whereas adult males either had a CY spigot or, more often, a non-functional CY nubbin. This indicates that potential CY use by males is at least largely limited to late juvenile instars and is not involved with egg sac construction. Despite the presence of CY spigots in both sexes, sexual dimorphism with respect to CYs was still evident since males lacked the CY spigot on each posterior lateral spinneret present in late juvenile and adult females, and CY spigots of males never had the wide shaft and opening of adult females. This study adds to our knowledge of spinning apparatus variability in modern spiders and demonstrates an exception to the paradigm that, in the CY spigot clade, such spigots are restricted to female spiders.

Copulatory mechanics in the wolf spider Agalenocosa pirity reveals a hidden diversity of locking systems in Lycosidae (Araneae).

Genital traits are among the fastest to evolve, and the processes that drive their evolution are intensively studied. Spiders are characterized by complex genitalia, but the functional role of the different structures during genital coupling is largely unknown. Members of one of the largest spider groups, the retrolateral tibial apophysis (RTA) clade, are characterized by a RTA on the male palp, which is thought to play a crucial role during genital coupling. However, the RTA was lost in several families including the species-rich wolf spiders (Lycosidae) leading to the hypothesis that the genital coupling is achieved by alternative mechanisms. Here, we investigate the genital interactions during copulation in the wolf spider Agalenocosa pirity (Zoicinae) on cryofixed mating pairs using electron, optical and X-ray microscopy and compare our findings with other lycosids and entelegyne spiders. We found an unprecedented coupling mechanism for lycosid spiders involving the palea and a membranous cuticle folding adjacent to the epigynal plate. Additionally, we show an uncommon coupling between the median apophysis and the contralateral genital opening, and confirmed that the terminal apophysis acts as functional conductor, as previously hypothesized for males of Zoicinae. Phylogenetic mapping of RTA indicated that the basal tibial process found in Agalenocosa is a secondary acquisition rather than a modified RTA.

Sperm competition tactics shape paternity: adaptive role of extremely long copulations in a wolf spider

Polyandry may occur in many species. In spiders when multiple males mate sequentially, conservative anatomical female traits largely, although not entirely, determine whether the first or last male gains precedence in siring the offspring. More flexible behavioural traits show remarkable variation among spiders, including the occurrence of extremely long copulation times. In the wolf spider Pardosa agrestis copulations can last several hours, even though complete fertilization of the female's eggs requires a small fraction of this time. We tested the hypothesis that long copulations in P. agrestis may be a way to overcome a strict first-male precedence, expected from the genital anatomy of female entelegyne spiders. In a large number of mating tests we observed complete and interrupted copulations in both positions of a double mating set-up. Using the sterile male technique we found that paternity was not exclusively determined by the mating order of males; interruption of mating had a dramatic effect on paternity, but did not affect offspring number in a single mating scenario (i.e. the copulation duration was sufficient for the fertilization of all eggs). Females that had an uninterrupted mating were less willing to mate again and became choosy, while females whose first mating was interrupted behaved similarly to virgin females. Also, males seemed to adjust copulation duration to female reproductive status, mating for less time with nonvirgin females, irrespective of whether the female's first mating was interrupted or not. We conclude that extremely long copulations are likely to be an adaptive behaviour manipulating female reproductive behaviour and enabling males to overcome phylogenetically determined limitations in paternity.

Spider Silk Processing for Spidroin Recovery from Crossopriza Lyoni Web

Spider silk is a potential biomaterial that can be used in various applications for its outstanding physicomechanical properties attributed by the spidroin composition. Efforts for commercializing spider silks have been mainly focused on the characterization of spidroins from the Entelegyne spiders for exceptional fibre construction. Hence, studies on silk proteins from the Haplogyne species remain neglected. The aim of this study is to isolate spidroin from Crossopriza lyoni web. Silk processing involved the pretreatment of fibres for the shell layer removal from the surface. A screening study was conducted to analyze the effect of temperature, incubation time and agitation speed on spidroin extraction using Ajisawa’s reagent by OFAT analysis followed by statistical optimization of the extraction process via RSM for maximal protein recovery. All parameters exerted significant effect on spidroin recovery (p<0.05) in which the maximum protein concentration (451.78 ± 0.110 µg/ml) was obtained at optimal condition of 70°C, 350 rpm and 1.25 hours. The discovery of spidroin from this study provides a basic platform for engineering spider silk to meet the demand for a variety of silk-based products in the near future.

Comparative female genital morphology in Stegodyphus spiders (Araneae: Eresidae)

The anatomy of the female genitalia sets the arena for sperm competition in species in which females mate multiply and store sperm. In spiders, females possess cuticular internal structures that have evolved into diverse sperm storage sites. Here, we investigate the female genital morphology of seven eresid spider species. We used X-ray micro-computed tomography for 3D reconstruction of the anatomy of the female genital system in the social Stegodyphus dumicola, S. mimosarum and S. sarasinorum, and the subsocial S lineatus, S. pacificus, S. tentoriicola as well as Eresus sandaliatus. We used histology to assess the sites of sperm storage in two selected species S. lineatus and S. dumicola. Our results show that the internal genitalia of the Stegodyphus species consist of two bilateral folds instead of closed ducts as often reported for entelegyne spiders. Along each fold, three regions are discriminable that differ in their specific morphology but are all surrounded by glandular tissue. Between species, the regions differ in shape and dimension. In virgin females, the lumina of all regions are filled with secretion. In mated females, spermatozoa were found in all three regions; however, only those sperm that are stored in the posterior region seem to become activated. Sperm found in anterior regions are embedded in a substance that might act as a mating plug. Our data suggest that the regions of the female genital tract differ in accessibility by the male as well as in their potential use for ejection and manipulation of sperm by the female.

Neurons and a sensory organ in the pedipalps of male spiders reveal that it is not a numb structure

The primary function of male copulatory organs is depositing spermatozoa directly into the female reproductive tract. Typical male copulatory organs are sensorily active. This is in contrast to the copulatory organs of male spiders (i.e. palpal bulbi), which have been assumed to lack nerves and muscles until recently. Neurons have been found within the bulbus of the spider Hickmania troglodytes, a taxon basal to all Neocribellata. We provide the first evidence for neurons and an internalized multi-sensillar sensory organ in the bulbus of an entelegyne spider (Philodromus cespitum). The sensory organ likely provides mechanical or chemical feedback from the intromitting structure, the embolus. We found further neurons associated with two glands within the bulbus, one of which is likely responsible for sperm extrusion during mating. These findings provide a new framework for studies on reproductive behaviour and sexual selection in spiders.

Comparative transcriptomics of Entelegyne spiders (Araneae, Entelegynae), with emphasis on molecular evolution of orphan genes.

Next-generation sequencing technology is rapidly transforming the landscape of evolutionary biology, and has become a cost-effective and efficient means of collecting exome information for non-model organisms. Due to their taxonomic diversity, production of interesting venom and silk proteins, and the relative scarcity of existing genomic resources, spiders in particular are excellent targets for next-generation sequencing (NGS) methods. In this study, the transcriptomes of six entelegyne spider species from three genera (Cicurina travisae, C. vibora, Habronattus signatus, H. ustulatus, Nesticus bishopi, and N. cooperi) were sequenced and de novo assembled. Each assembly was assessed for quality and completeness and functionally annotated using gene ontology information. Approximately 100 transcripts with evidence of homology to venom proteins were discovered. After identifying more than 3,000 putatively orthologous genes across all six taxa, we used comparative analyses to identify 24 instances of positively selected genes. In addition, between ~ 550 and 1,100 unique orphan genes were found in each genus. These unique, uncharacterized genes exhibited elevated rates of amino acid substitution, potentially consistent with lineage-specific adaptive evolution. The data generated for this study represent a valuable resource for future phylogenetic and molecular evolutionary research, and our results provide new insight into the forces driving genome evolution in taxa that span the root of entelegyne spider phylogeny.

Observations on germ band development in the cellar spider Pholcus phalangioides.

Most recent studies of spider embryonic development have focused on representatives of the species-rich group of entelegyne spiders (over 80% of all extant species). Embryogenesis in the smaller spider groups, however, is less well studied. Here, we describe the development of the germ band in the spider species Pholcus phalangioides, a representative of the haplogyne spiders that are phylogenetically the sister group of the entelegyne spiders. We show that the transition from radially symmetric embryonic anlage to the bilaterally symmetric germ band involves the accumulation of cells in the centre of the embryonic anlage (primary thickening). These cells then disperse all across the embryonic anlage. A secondary thickening of cells then appears in the centre of the embryonic anlage, and this thickening expands and forms the segment addition zone. We also confirm that the major part of the opisthosoma initially develops as a tube shaped structure, and its segments are then sequentially folded down on the yolk during inversion. This special mode of opisthosoma formation has not been reported for entelegyne spiders, but a more comprehensive sampling of this diverse group is necessary to decide whether this peculiarity is indeed lacking in the entelegyne spiders.

Neofunctionalization of a Duplicate dachshund Gene Underlies the Evolution of a Novel Leg Segment in Arachnids.

The acquisition of a novel function, or neofunctionalization, protects duplicated genes from redundancy and subsequent loss, and is a major force that drives adaptive evolution. Neofunctionalization has been inferred for many duplicated genes based on differences in regulation between the parental gene and its duplicate. However, only few studies actually link the new function of a duplicated gene to a novel morphological or physiological character of the organism. Here we show that the duplication of dachshund (dac) in arachnids (spiders and allies) is linked with the evolution of a novel leg segment, the patella. We have studied dac genes in two distantly related spider species, the entelegyne spider Parasteatoda tepidariorum and the haplogyne spider Pholcus phalangioides. Both species possess two paralogous dac genes that duplicated before the split between entelegyne and haplogyne spiders. In contrast to the evolutionarily highly conserved dac1, its duplicate dac2 is strongly expressed in the patella leg segment during embryogenesis in both species. Using parental RNA interference in P. tepidariorum we show that dac2 is required for the development of the patella segment. If dac2 function is impaired, then the patella is fused with the tibia into a single leg segment. Thus, removing the function of dac2 experimentally reverts P. tepidariorum leg morphology into a stage before the duplication of dac and the evolution of the patella segment. Our results indicate that the origin of the patella is the result of the duplication and subsequent neofunctionalization of dac in the arachnid lineage.

Comparative Cytogenetics of Seven Ctenidae Species (Araneae)

The present study elevates the number of cytogenetically analyzed ctenid species and genera from two to eight and six, respectively, presenting comparisons between chromosomal data obtained and the phylogenetic hypothesis proposed in the literature. Six ctenid species presented 13 autosomal pairs, exhibiting either X1X2O (Ctenus ornatus, Ctenus sp., Parabatinga brevipes and Phoneutria nigriventer) or X1X2X3O sex chromosome systems (Nothroctenus sp. and Viracucha andicola). Asthenoctenus borellii showed 2n ♂ = 20 + X1X2O. In all species, the chromosomes were telocentric. Some cells of one C. ornatus specimen exhibited one extra chromosome that, considering the behavioral similarities between the two chromosomes, can be considered to be supernumerary, derived from or giving rise to a sex chromosome. Silver impregnation revealed nucleolar organizer regions on one autosomal pair of C. ornatus and P. nigriventer (Cteninae) and two pairs of V. andicola (Acanthocteninae). Chromosomal data suggests that the X1X2X3O system arose several times in the evolution of entelegyne spiders, and that conversion of an X1X2O system into an X1X2X3O system and vice-versa has been a relatively common event in spiders. All the chromosomal data corroborate the close relationship between Ctenus and Phoneutria, the placement of P. brevipes within Cteninae, the placement of Anahita in a separated branch within Cteninae, and the inclusion of A. borellii in a distinct group within the ctenids (Viridasiinae), all of which are as proposed by phylogenetic hypotheses available in the literature.

Multiple origins of sex chromosome fusions correlated with chiasma localization in Habronattus jumping spiders (Araneae: Salticidae).

Entelegyne spiders rarely show fusions yielding neo‐Y chromosomes, which M. J. D. White attributed to a constraint in spiders, namely their proximal chiasma localization acting to upset meiotic segregation in males with fusions. Of the 75 taxa of Habronattus and outgroups studied, 47 have X1X20 sex chromosomes in males, 10 have X1X2Y, 15 have X1X2X3Y, 2 have X0, and one has both X1X20 and X1X2X3Y. Chromosome numbers and behavior suggest neo‐Ys formed by an autosome‐X fusion to make X1X2Y, with a second fusion to an autosome to make X1X2X3Y. Phylogeny shows at least 8–15 gains (or possibly some losses) of neo‐Y (i.e., X‐autosome fusions), a remarkable number for such a small clade. In contrast to the many X‐autosome fusions, at most one autosome–autosome fusion is indicated. Origins of neo‐Y are correlated significantly with distal localization of chiasmata, supporting White's hypothesis that evolution of neo‐Y systems is facilitated by looser pairing (distal chiasmata) at meiosis. However, an alternative (or contributing) explanation for the correlation is that X‐autosome fusions were selected to permit isolation of male‐favored alleles to the neo‐Y chromosome, aided by distal chiasmata limiting recombination. This intralocus sexual conflict hypothesis could explain both the many X‐autosome fusions, and the stunning complexity of male Habronattus courtship displays.

Sequential origin in the high performance properties of orb spider dragline silk

Major ampullate (MA) dragline silk supports spider orb webs, combining strength and extensibility in the toughest biomaterial. MA silk evolved ~376 MYA and identifying how evolutionary changes in proteins influenced silk mechanics is crucial for biomimetics, but is hindered by high spinning plasticity. We use supercontraction to remove that variation and characterize MA silk across the spider phylogeny. We show that mechanical performance is conserved within, but divergent among, major lineages, evolving in correlation with discrete changes in proteins. Early MA silk tensile strength improved rapidly with the origin of GGX amino acid motifs and increased repetitiveness. Tensile strength then maximized in basal entelegyne spiders, ~230 MYA. Toughness subsequently improved through increased extensibility within orb spiders, coupled with the origin of a novel protein (MaSp2). Key changes in MA silk proteins therefore correlate with the sequential evolution high performance orb spider silk and could aid design of biomimetic fibers.

The diversity and evolution of chelicerate hemocyanins.

BackgroundOxygen transport in the hemolymph of many arthropod species is facilitated by large copper-proteins referred to as hemocyanins. Arthropod hemocyanins are hexamers or oligomers of hexamers, which are characterized by a high O2 transport capacity and a high cooperativity, thereby enhancing O2 supply. Hemocyanin subunit sequences had been available from horseshoe crabs (Xiphosura) and various spiders (Araneae), but not from any other chelicerate taxon. To trace the evolution of hemocyanins and the emergence of the large hemocyanin oligomers, hemocyanin cDNA sequences were obtained from representatives of selected chelicerate classes.ResultsHemocyanin subunits from a sea spider, a scorpion, a whip scorpion and a whip spider were sequenced. Hemocyanin has been lost in Opiliones, Pseudoscorpiones, Solifugae and Acari, which may be explained by the evolution of trachea (i.e., taxon Apulmonata). Bayesian phylogenetic analysis was used to reconstruct the evolution of hemocyanin subunits and a relaxed molecular clock approach was applied to date the major events. While the sea spider has a simple hexameric hemocyanin, four distinct subunit types evolved before Xiphosura and Arachnida diverged around 470 Ma ago, suggesting the existence of a 4 × 6mer at that time. Subsequently, independent gene duplication events gave rise to the other distinct subunits in each of the 8 × 6mer hemocyanin of Xiphosura and the 4 × 6mer of Arachnida. The hemocyanin sequences were used to infer the evolutionary history of chelicerates. The phylogenetic trees support a basal position of Pycnogonida, a sister group relationship of Xiphosura and Arachnida, and a sister group relationship of the whip scorpions and the whip spiders.ConclusionFormation of a complex hemocyanin oligomer commenced early in the evolution of euchelicerates. A 4 × 6mer hemocyanin consisting of seven subunit types is conserved in most arachnids since more than 400 Ma, although some entelegyne spiders display selective subunit loss and independent oligomerization. Hemocyanins also turned out to be a good marker to trace chelicerate evolution, which is, however, limited by the loss of hemocyanin in some taxa. The molecular clock calculations were in excellent agreement with the fossil record, also demonstrating the applicability of hemocyanins for such approach.

Securing paternity in spiders? A review on occurrence and effects of mating plugs and male genital mutilation

Low female mating frequencies often appear to be cases of direct male induction that can oppose female interests. Mating plugs are most obvious means leading to low degrees of multiple mating in females. In spiders, mating plugs are formed by a variety of amorphous materials, by the breakage of the male sperm transferring organ, or by the whole male that functions as a mating barrier. Our compilation of the available information on the presence of the various types of mating plugs suggests that plugs predominantly occur in entelegyne spiders. In this group, plugs do not interfere with oviposition since separate openings for insemination and oviposition are present. In contrast, mating plugs seem to be rare in haplogyne spiders that do not possess separate openings. The available experimental studies on the function of the different types of plugs suggest that plugs can be considered as male adaptations to avoid sperm competition. However, females in some cases were shown to have evolved means to prevent or control male manipulation or may selectively favour plug production in specific males, an aspect which has largely been neglected. In order to understand plug evolution and function we need to explore the morphological, behavioural and biochemical aspects involved and extend our approach to interactions between the sexes.

CHROMOSOMES OF CROSSOPRIZA LYONI (BLACKWALL 1867), INTRAINDIVIDUAL NUMERICAL CHROMOSOME VARIATION IN PHYSOCYCLUS GLOBOSUS (TACZANOWSKI 1874), AND THE DISTRIBUTION PATTERN OF NORs (ARANEOMORPHAE, HAPLOGYNAE, PHOLCIDAE)

Abstract Pholcidae (Haplogynae) encompasses 967 described species, of which only 14 have been cytogenetic analyzed. Several chromosomal features have already been described including presence of meta- and sub-metacentric chromosomes and sex determination chromosome system (SDCS) of the X, X1X2Y, and X1X2 types, which contrast with the telo- and acrocentric chromosomes and SDCS of the X1X2 type typical of entelegyne spiders. To obtain further cytogenetic information for the family, we examined two pholcid species, Crossopriza lyoni (Blackwall 1867) and Physocyclus globosus (Taczanowski 1874) using both conventional staining and silver staining techniques. Crossopriza lyoni exhibited 2n = 23 = 22 + X in males and 2n = 24 = 22 + XX in females, while P. globosus showed 2n = 15 = 14 + X and 4n = 30 = 28 + 2X, both in male adults, 2n = 16 = 14 + XX in female adults and embryos, and 2n = 15 = 14 + X in male embryos. Both species revealed predominately metacentric and submetacentric chromosomes and a SDCS of the ...